What is the recommended dose of Keflex (cephalexin) for a child weighing 33 pounds with bullous impetigo?

Cephalexin Dosing for Bullous Impetigo in a 33-pound Child

For a child weighing 33 pounds (15 kg) with bullous impetigo, the recommended dose of cephalexin is 25-50 mg/kg/day divided into 3-4 doses, which equals 375-750 mg per day total, or approximately 125-250 mg per dose given 3-4 times daily. 1

Dosing Calculation

To determine the appropriate cephalexin dose:

• Child's weight: 33 pounds = 15 kg
• Recommended dosage range: 25-50 mg/kg/day 1
• Total daily dose: 375-750 mg/day

Dosing options:

1. Four times daily regimen (preferred for impetigo):

   • 94-188 mg per dose (rounded to 100-200 mg) given every 6 hours

2. Three times daily regimen (alternative):

   • 125-250 mg per dose given every 8 hours

Administration Considerations

• Formulation: Cephalexin suspension is available in 125 mg/5 mL and 250 mg/5 mL concentrations 2
• Duration: Treatment should continue for 7 days 1
• Administration: Can be given with or without food
• Storage: After reconstitution, the suspension should be refrigerated and is stable for 14 days 2

Evidence for Cephalexin in Bullous Impetigo

Cephalexin is highly effective for bullous impetigo, which is predominantly caused by Staphylococcus aureus:

• The Infectious Diseases Society of America (IDSA) guidelines specifically recommend cephalexin as a first-line treatment for impetigo 1
• Studies have demonstrated cephalexin's superior efficacy compared to penicillin for impetigo, with treatment failure rates of 0% for cephalexin versus 24% for penicillin V 3
• Cephalexin has excellent activity against both S. aureus and Streptococcus pyogenes, the primary pathogens in impetigo 4

Practical Dosing Tips

• For a 15 kg child using the 125 mg/5 mL suspension:

  • 1-2 teaspoons (5-10 mL) four times daily 2
  • OR 1.5-2 teaspoons (7.5-10 mL) three times daily

• For a 15 kg child using the 250 mg/5 mL suspension:

  • 0.5-1 teaspoon (2.5-5 mL) four times daily 2
  • OR 0.75-1 teaspoon (3.75-5 mL) three times daily

Important Clinical Considerations

• Monitoring: Watch for clinical improvement within 48-72 hours
• Common side effects: Diarrhea (most common), nausea, rash
• Allergies: Confirm absence of cephalosporin allergy before prescribing
• Alternative options if cephalexin cannot be used:
  • Clindamycin: 20 mg/kg/day in 3 divided doses 1
  • Mupirocin ointment: For limited lesions, apply twice daily 1

Pitfalls to Avoid

• Underdosing: Using adult dosing (250 mg QID) rather than weight-based dosing can lead to treatment failure
• Inadequate duration: Stopping therapy prematurely can lead to recurrence
• Overlooking MRSA: If no improvement occurs within 48-72 hours, consider MRSA coverage
• Compliance issues: Four-times-daily dosing may be challenging; ensure caregivers understand the importance of adherence to the prescribed regimen

While three-times-daily dosing may improve compliance 5, the IDSA guidelines specifically recommend 3-4 divided doses for impetigo in children, with four-times-daily dosing being the traditional approach for optimal coverage 1.